fn div(x: i32, y: i32) -> i32 {
    if y == 0 {
        panic!("division by zero");
    } else {
        x / y
    }
}
fn main() {
//     堆分配的整数
    let _x = Box::new(0i32);
    div(3, 0);
    println!("This point won't be reached");
//     `_x`应当会在此处被销毁
}
// run:
//     cargo run
// valgrind --leak-check=full ./target/debug/option_result_panic_3